In this study, in order to evaluate the benefits of the application of functional braces that reduce weight load, we examined pain as well as the length of the use of a functional brace from the preoperative period to 2 months postoperative, by classifying patients based on the severity of cartilage lesions. The clinical efficacy of a functional brace was evaluated in patients with osteoarthritis of the knee (OA group) and internal derangement of the knee (ID group) who used braces, using the subjective functional evaluation index of Western Ontario and McMaster Universities (WOMAC). In addition, the strength of knee muscles was measured using a hand held dynamometer (HHD), and the duration of one foot standing with eyes open was examined comparatively. The OA group was observed pain at 2 months postoperative, a longer non-weight bearing period, and longer time until weaning from braces. However, no significant difference was observed in the aspect of clinical efficacy that was evaluated from the results of pain and physical function in the WOMAC index; the scores of both groups were favorable. Regarding the muscle force from HHD data, significant relations were partly observed between affected and non-affected sides in each of the OA group and the ID group. The duration of one-foot standing with eyes open was significantly lower for the affected side compared with the non-affected side. The benefits of the brace in patients with knee cartilage injury who used a functional brace after were confirmed, and it was suggested that the physical ability of these patients could be improved further by providing instruction regarding home exercises for the maintenance and strengthening of muscular strength and balancing ability.